Semiconductor devices using nitride semiconductors or silicon carbide (SiC) as base materials are receiving attention. The reason is that these materials have band gaps that are larger than that of silicon, and thus may be used to achieve semiconductor devices with higher breakdown voltages than silicon based devices. However, although the breakdown voltage of the material is high, if the dielectric breakdown voltage of an electrode and surrounding dielectric structure provided on the corresponding material is low, it is impossible to take advantage of the material. For this reason, an electrode structure appropriate for a wide-band gap semiconductor is required.